Various types of protectors have been designed and manufactured in the past for protecting coaxial transmission lines and associated equipment from damage due to transient surge voltages caused by lightning and induced AC power voltages.
The expansion of services on coaxial based network to include voice, video and data requires increased system reliability and transmission continuity. Broadband coaxial systems require a protector to handle surges and protect expensive electronic equipment without disturbing transmission signals.
These protectors generally consist of a gas discharge tube connected between the center conductor and the braided shield of the coaxial cable. The protectors include a housing which consists of a metal block, normally made of aluminum or brass, which is bored to include a passage for a center conductor and an enlarged cavity for housing the gas tube. The housing serves primarily as a mounting for a standardized gas tube and for the input and output connectors which are attached to the housing. The resulting protector is large in size, expensive to manufacture and generally adds considerable capacitance which requires extraordinary methods to match the impedance of the protector to the characteristic impedance of the coaxial transmission line.
The need for miniature, low cost and microwave transparent surge protectors has not been provided by the available devices. Several patents show available surge protectors. The patents include U.S. Pat. Nos. 4,633,359; 4,544,984; 4,509,090; and 4,409,637. The protectors disclosed in these patents generally consist of a discrete, "off-the-shelf" or "universal-type" gas tube which have been adapted for use in coaxial protector application. These gas tubes are generally of a universal-type construction and are not optimized for coaxial circuit protection. Use of these universal-type gas tubes for coaxial circuit protection results in poor microwave signal transmission and requires the use of complex configurations to compensate for the mismatch which is created by the relatively high capacitance of the gas tube and housing to the characteristic impedance of the coaxial line.
An example of this mismatch problem can be seen in U.S. Pat. No. 4,409,637 in which the description goes to great lengths to teach methods for creating a matched condition for the discrete universal type commercial gas tube utilized in the protector shown therein. The elaborate method of impedance matching and the housing needed to contain the gas tube greatly inflate the cost of the device as shown in the '637 patent.